We have obtained crystals of two new ligand-receptor complexes of the cytokine receptor superfamily. The 1st complex is of ovine prolactin bound to two prolactin receptor extracellular domains. The first structure of this complex will be of great interest to understand the specificity profiles of human growth hormone (hGH) and prolactin and their receptors. It will provide the missing information between the complexes hGH bound to its own receptor and to the prolactin receptor. The 2nd complex is that between an inferon -g variant in complex with a single copy of its receptor a-chain. We want to assess the quality of our prolactin/prolactin receptor complex crystals. We have small but highly polarizable crystals, for which we see diffraction spots at 4.5 E "in-house". We need to assess their diffraction quality with extremely bright radiation. We also want to find out what resolution is achievable for our inferon -g/receptor-a complex crystals.